1. Field
The present invention relates to communications. More particularly, the present invention relates to a novel and improved method and apparatus for providing broadcast short message services.
2. Background
In communication systems, a central communications center transmits data to remote subscriber stations. In order to efficiently use a limited communications resource, the communications resource is divided into sub-bands and channels. A typical allocation of channels would include a pilot channel, a synchronization channel providing necessary timing information, a plurality of traffic channels for conducting point to point communications and a plurality of paging channels associated with the traffic channels for providing signaling data.
Typically, when a subscriber station registers with the central communications center, the central communications center informs the subscriber station which paging channel of the plurality of available paging channels to monitor. When the central communications center needs to set up a point to point communication with a subscriber station it transmits a traffic page on the paging channel being monitored by the subscriber station. The traffic page would typically comprise subscriber station identification information and traffic channel identification information. In response to the received traffic page, the identified subscriber station would prepare to conduct point to point communications on the identified traffic channel.
Power consumption is an important consideration of the subscriber stations, particularly in the case of mobile subscriber stations. In order to reduce the power consumption of the subscriber stations, a method known as slotted paging was devised. Slotted paging in a spread spectrum communications system is described in detail in U.S. patent application Ser. No. 07/847,149, now U.S. Pat. No. 5,392,287 issued on Feb. 21, 1995 to Geib et al., assigned to assignee of the present invention and incorporated by reference herein. By this technique a subscriber station monitors its assigned paging channel at predetermined intervals, which results in a significant power savings relative to monitoring the paging channel continuously.
The central communications center must know a priori the time slots when the subscriber station will monitor the paging channel, and must reserve all pages for that subscriber station for these slots. When the paging channel is monitored at intervals, the system is referred to as slotted paging, whereas when the paging channel is continuously monitored it is referred to as non-slotted paging. The periods when the subscriber station is not monitoring the paging channel can vary from subscriber station to subscriber station depending on the needs of the subscriber station user.
The expression slotted paging comes from dividing time into slots of a predetermined duration. In a slotted paging system, the subscriber station monitors a slot, it will again monitor a subsequent slot an integral number slots in the future. The number of slots between periodically monitored slots is referred to as the slot cycle.
In addition, it is possible to send very short messages over the paging channel to subscriber stations. It is, however, important to keep the length of such messages to a minimum because the paging channel resource is a shared resource and by its nature scarce.
In the communications industry there is a need to be able to transmit broadcast messages. Broadcast messages are messages that are provided to all users in a local area. For example a weather service, may provide weather forecasts to all the subscriber stations in a given area. The use of slotted paging provides a challenge to providing broadcast message in such a way that they can be received by all of the subscriber stations in the area.